1. Field of the Invention
The present invention relates in general to the field of electronics and lighting, and more specifically to a system and method to controlling and/or providing power to current regulated light sources, such as light emitting diode light sources.
2. Description of the Related Art
Commercially practical incandescent light bulbs have been available for over 100 years. However, other light sources show promise as commercially viable alternatives to the incandescent light bulb. Light emitting diodes (LEDs) are becoming particularly attractive as main stream light sources in part because of energy savings through high efficiency light output, long life, and environmental incentives such as the reduction of mercury. The efficiency and intensity of LEDs continues to improve. Multiple applications exist for LEDs, and the number of applications continues to increase. For example, LEDs can be used for ordinary indoors and outdoors illumination, television backlighting, large form-factor video displays, etc.
LEDs are semiconductor devices and are driven by direct current. The intensity of the LED varies in direct proportion to the current flowing through the LED. Thus, increasing current supplied to an LED increases the intensity of the LED and decreasing current supplied to the LED dims the LED.
FIG. 1 depicts a multi-channel LED driver and controller system 100 that controls current in parallel connected LEDs. The LED driver and controller system 100 includes 16-channel LED drivers 102.0 through 102.M (collectively referred to as “LED drivers 102”), where M+1 represents the number of LED drivers 102 in LED driver and controller system 100 and M is a positive number. LED controller 104 controls the LED drivers 102. LED driver 102.0 includes 16 output control signals OUT0-OUT15 generated by I/O and controller 103.0 to control conductivity of respective switches 106.0-106.15. In at least one embodiment, switches 106.0-106.15 are bipolar junction transistors.
The switches 106.0-106.15 are respectively connected in series with LEDs 108.0-108.15. Thus, when switches 106.0-106.15 conduct, LED currents iL0-iL15 flow through respective LEDs 108.0-108.15. The LEDs 106.0-106.15 can be individually controlled by individually controlling the conductivity of respective switches 106.0-106.15. The output control signals OUT0-OUT15 are pulse width modulated signals. Controlling the pulse widths of output control signals OUT0-OUT15 controls the respective averages of respective LED currents iL0.0-iL15.0 for respective LEDs 108.0-108.15 and LED currents iL0.M-iL15.M for respective LEDs 112.0-112.15. Controlling the respective averages of respective LED currents iL0-iL15 controls the intensity of respective LEDs 108.0-108.15. LEDs 108.0-108.15 can be color mixed with red, green, and blue LEDs. Including multi-colored combinations of LEDs 108.0-108.15 and coordinating the pulse widths of output control signals allows multi-channel LED driver and controller system 100 to generate a large array of colors and intensity of LEDs 108.-108.15. The configuration of LED driver 102.0 is repeated by the M LED drivers 102. For example, LED driver 102.M includes output signals OUT0-OUT15 and switches 110.0-110.15 to control LED currents in LEDs 112.0-112.15.
LED controller 104 can coordinate control of output signals OUT0-OUT15 for LED drivers 102.0-102.15 by providing data directly to the LED drivers 102.0-102.15 via respective parallel data buses 114.0-114.15. The LED controller provides serial data to LED driver 102.0 via serial data line 115.0. The LED driver and controller system 100 also includes serial data bus 115.1-115.15 that provide serial data from one LED driver to the next LED driver and finally back to LED controller 104 from LED driver 102.M via serial data bus 115.16.
Texas Instruments, Inc.'s part number TLC5940 represents one example of an LED driver, such as each of LED drivers 102. The data sheet for the TLC5940 16-channel LED driver describes functionality of the TLC5940 and an exemplary configuration of LED driver and controller system 100. The data sheet for the TLC5940 is entitled “16 Channel LED Driver with DOT Correction and Grayscale PWM Control”, dated December 2004-revised October 2007, is available from Texas Instruments, Inc., a Texas, USA, corporation.
Because all of LEDs connected to an LED driver in LED driver and controller system 100 are connected in parallel, the LED currents iL0-iL15 for each of LED drivers 102 are relatively high. Additionally, each of LED drivers 102 has a voltage drop, such as 1-1.5 volts. Thus, LED driver and controller system 100 generally has a low system efficiency. It would be desirable to, for example, improve the efficiency of LED driver and controller system 100.